The fractionation of sea salt and acids during transport across an Antarctic ice shelf

first_imgAnalyses of Cl−, NO3−, SO42−, Na and Mg made on a series of surface snow samples, collected at 4 km intervals along a 116 km traverse of the Fimbul Ice Shelf in Dronning Maud Land, show that fractionation of some of the sea salt species has taken place. There is depletion of Mg compared to Na in the coastal part of the traverse, but the bulk sea water ratio is maintained further inland. Evidence for Cl− fractionation is less clear, with a depletion in some sections and an enrichment in others compared to Na. Taken over the whole data-set of 120 samples, the bulk sea water ratio between the marine ions Na, Mg and Cl appears to be conservatively maintained. For all of the sea-salt components, the general trend in concentration was an increase from the ice shelf front to a maximum value approximately 45 km inland, before decreasing to a value of 10% of the maximum by the end of the traverse. Non sea-salt sulphate followed a similar trend to 45 km, but the subsequent decrease in concentration was less rapid, suggesting a greater residence time for sulphate derived from marine biogenic activity than for sea-salt aerosol. Relatively high concentrations of nitrate were found in all of the surface snow samples in comparison to samples taken from shallow pits at each end of the traverse. This may be an indication of a post depositional loss of nitrate from the snow surface.last_img read more

High spatial and temporal resolution observations of the ionospheric cusp

first_imgThe Halley PACE HF radar has been operated in a new mode to provide very high time (10 s) and space (15 km) resolution measurements of the iono-spheric signatures of the cusp and the low-latitude boundary layer. The first data show that the iono-spheric signature of flux transfer events occur up to 300 km equatorward of regions showing the HF characteristics of the ionospheric cusp. Whilst larger flux transfer events are seen, on average, every 7 min, many much smaller and short-duration events have been identified. On one occasion DMSP data have been used to show that at least four flux transfer events are occurring simultaneously at the edge of the cusp over 2 h of MLT. There is strong, but not conclusive evidence, that reconnection at the magnetopause is both intermittent and patchy. These data also suggest that flux transfer events can be a significant contributor to the cross-polar cap potential.last_img read more

Sulphur sources for epithermal and mesothermal veins in Cretaceous-Tertiary magmatic-arc rocks, Livingston Island, South Shetland Islands

first_imgEpithermal veins in early Triassic turbidites on Hurd Peninsula are isotopically homogeneous over an area of 13 km × 2 km (mean δ34S = +2.2‰, 1σ= 1.7, n = 65) suggesting derivation from a deep circulating, neutral-chloride hydrothermal plume containing magmatic sulphur. The sense of fractionation (pyrite = +3.5, arsenopyrite = +3.2, sphalerite = +2.9, chalcopyrite = +2.5, galena = +0.9‰) and isotopic temperatures between 250 and 345°C suggest partial isotopic equilibration. Sulphides in massive dark carbonate/peperitic dyke breccias, with abundant magnetite, hematite and titanite and traces of barite, garnet, zircon and monazite are isotopically heavy (+7 to +14.9‰, n = 12) due either to dyke intrusion into the hydrothermal system resulting in degassing of H2S, or to a second, isotopically heavy and sulphate-bearing solution in fault zones along which dykes were subsequently intruded. Vein sulphides in nearby Cretaceous volcanic rocks are similar to the epithermal system (mean = + 1.8‰, 1σ = 0.9, n = 6, pyrite = +2.0, chalcopyrite = +1.5), suggesting sulphur-derivation by degassing of sub-volcanic magma, or remobilization of disseminated sulphides during plutonism. Sulphide in an Eocene tonalite pluton is slightly 32S-enriched (mean = 0‰, 1σ = 1.9, n =7, molybdenite = +0.7, pyrite = +1.5, chalcopyrite = –2.6) and was exsolved directly from the cooling tonalitic magma.last_img read more

Atmospheric signals and characteristics of accumulation in Dronning Maud Land, Antarctica

first_imgWith the planned European Programme for Ice Coring in Antarctica in Dronning Maud Land it is important to understand the processes leading to accumulation for successful interpretation of core data. Because it is impractical to obtain precipitation observations with a large spatial coverage and on a daily timescale in Antarctica, model-generated precipitation must be considered for a comprehensive study of the region. However, without observational data it is difficult to check the veracity of the model data. Precipitation data from the European Centre for Medium-Range Weather Forecasts reanalysis project shows that 89% of days have low (under 0.2 mm) precipitation resulting in 31% of the annual total. At the other extreme, less than 1% of days have high (over 1 mm) precipitation, which results in 20% of the annual total. It is reasoned that the changes in the frequency of extreme precipitation events could alter the trace record in ice cores and lead to a bias in reconstructed paleotemperatures. Case studies reveal that high-precipitation days have amplified upper level planetary waves directing warm moist air to the region. Associated with this is the presence of a cyclone in or at the northeast extreme of the Weddell Sea. Commonly, the longwaves provide a blocked anticyclone in the South Atlantic to form a dipolar channeling of the air mass. The accumulation variability is linked to the variability in the intensity of these storms and their tracks. It is seen that this is related to the El Niño-Southern Oscillation and a semiannual cycle.last_img read more

Scaling of solar wind epsilon and the AU, AL and AE indices by WIND

first_imgWe apply the finite size scaling technique to quantify the statistical properties of fluctuations in AU, AL and AE indices and in the epsilon parameter that represents energy input from the solar wind into the magnetosphere. We find that the exponents needed to rescale the probability density functions (PDF) of the fluctuations are the same to within experimental error for all four quantities. This self-similarity persists for time scales up to similar to4 hours for AU, AL and epsilon and up to similar to2 hours for AE. Fluctuations on shorter time scales than these are found to have similar long-tailed (leptokurtic) PDF, consistent with an underlying turbulent process. These quantitative and model-independent results place important constraints on models for the coupled solar wind-magnetosphere system.last_img read more

Radar-derived bed roughness characterization of Institute and Möller ice streams, West Antarctica, and comparison with Siple Coast ice streams

first_imgSubglacial bed conditions exert a significant control on ice stream behavior and evolution, and can be characterized by determining bed roughness from FFT analysis of radar-imaged basal reflectors. Here we assess bed roughness across Institute and Moller ice streams, West Antarctica, and compare our findings with bed roughness determined across the Siple Coast ice streams. We find that variations in bed roughness are spatially organized, and attribute this to the varying efficacy of subglacial erosion and deposition, with rougher (inland, slow-flowing) regions largely manifesting preglacial topography, and smoother (downstream, fast-flowing) regions evincing significant postglacial modification to the subglacial landscape. The observed similarities between bed roughness characteristics of IIS/MIS and the Siple ice streams suggest that IIS and MIS are largely underlain by wet, poorly consolidated sediments, and may therefore be vulnerable to the types of dynamical instabilities experienced by the Siple ice streams.last_img read more

Autonomous underwater vehicles (AUVs) and investigations of the ice–ocean interface in Antarctic and Arctic waters

first_imgLimitations of access have long restricted exploration and investigation of the cavities beneath ice shelves to a small number of drillholes. Studies of sea-ice underwater morphology are limited largely to scientific utilization of submarines. Remotely operated vehicles, tethered to a mother ship by umbilical cable, have been deployed to investigate tidewater-glacier and ice-shelf margins, but their range is often restricted. The development of free-flying autonomous underwater vehicles (AUVs) with ranges of tens to hundreds of kilometres enables extensive missions to take place beneath sea ice and floating ice shelves. Autosub2 is a 3600 kg, 6.7 m long AUV, with a 1600 m operating depth and range of 400 km, based on the earlier Autosub1 which had a 500m depth limit. A single direct-drive d.c. motor and five-bladed propeller produce speeds of 1-2 ms−1. Rear-mounted rudder and stern-plane control yaw, pitch and depth. The vehicle has three sections. The front and rear sections are free-flooding, built around aluminium extrusion space-frames covered with glass-fibre reinforced plastic panels. The central section has a set of carbon-fibre reinforced plastic pressure vessels. Four tubes contain batteries powering the vehicle. The other three house vehicle-control systems and sensors. The rear section houses subsystems for navigation, control actuation and propulsion and scientific sensors (e.g. digital camera, upward-looking 300 kHz acoustic Doppler current profiler, 200 kHz multibeam receiver). The front section contains forward-looking collision sensor, emergency abort, the homing systems, Argos satellite data and location transmitters and flashing lights for relocation as well as science sensors (e.g. twin conductivity-temperature-depth instruments, multibeam transmitter, sub-bottom profiler, AquaLab water sampler). Payload restrictions mean that a subset of scientific instruments is actually in place on any given dive. The scientific instruments carried on Autosub are described and examples of observational data collected from each sensor in Arctic or Antarctic waters are given (e.g. of roughness at the underside of floating ice shelves and sea ice).last_img read more

Freshwater fluxes in the Weddell Gyre: results from δ18O

first_imgFull-depth measurements of δ18O from 2008 to 2010 enclosing the Weddell Gyre in the Southern Ocean are used to investigate the regional freshwater budget. Using complementary salinity, nutrients and oxygen data, a four-component mass balance was applied to quantify the relative contributions of meteoric water (precipitation/glacial input), sea-ice melt and saline (oceanic) sources. Combination of freshwater fractions with velocity fields derived from a box inverse analysis enabled the estimation of gyre-scale budgets of both freshwater types, with deep water exports found to dominate the budget. Surface net sea-ice melt and meteoric contributions reach 1.8% and 3.2%, respectively, influenced by the summer sampling period, and −1.7% and +1.7% at depth, indicative of a dominance of sea-ice production over melt and a sizable contribution of shelf waters to deep water mass formation. A net meteoric water export of approximately 37 mSv is determined, commensurate with local estimates of ice sheet outflow and precipitation, and the Weddell Gyre is estimated to be a region of net sea-ice production. These results constitute the first synoptic benchmarking of sea-ice and meteoric exports from the Weddell Gyre, against which future change associated with an accelerating hydrological cycle, ocean climate change and evolving Antarctic glacial mass balance can be determined.last_img read more

New constraints on the timing of West Antarctic ice sheet retreat in the eastern Amundsen Sea since the Last Glacial Maximum

first_imgGlaciers flowing into the Amundsen Sea Embayment (ASE) account for > 35% of the total discharge of the West Antarctic Ice Sheet (WAIS) and have thinned and retreated dramatically over the past two decades. Here we present detailed marine geological data and an extensive new radiocarbon dataset from the eastern ASE in order to constrain the retreat of the WAIS since the Last Glacial Maximum (LGM) and assess the significance of these recent changes. Our dating approach, relying mainly on the acid insoluble organic (AIO) fraction, utilises multi-proxy analyses of the sediments to characterise their lithofacies and determine the horizon in each core that would yield the most reliable age for deglaciation. In total, we dated 69 samples and show that deglaciation of the outer shelf was underway before 20,600 calibrated years before present (cal yr BP), reaching the mid-shelf by 13,575 cal yr BP and the inner shelf to within ca. 150 km of the present grounding line by 10,615 cal yr BP. The timing of retreat is broadly consistent with previously published radiocarbon dates on biogenic carbonate from the eastern ASE as well as AIO 14C ages from the western ASE and provides new constraints for ice sheet models. The overall retreat trajectory – slow on the outer shelf, more rapid from the middle to inner shelf – clearly highlights the importance of reverse bedslopes in controlling phases of accelerated groundling line retreat. Despite revealing these broad scale trends, the current dataset does not capture detailed changes in ice flow, such as stillstands during grounding line retreat (i.e., deposition of grounding zone wedges) and possible readvances as depicted in the geomorphological record.last_img read more

The Antarctic Peninsula under a 1.5°C global warming scenario.

first_imgWarming of the Antarctic Peninsula in the latter half of the 20th century was greater than any other terrestrial environment in the Southern Hemisphere, and obvious cryospheric and biological consequences have been observed. Under a global 1.5°C scenario, warming in the Antarctic Peninsula is likely increase the number of days above 0°C, with up to 130 of such days each year in the northern Peninsula. Ocean turbulence will increase, making the circumpolar deep water (CDW) both warmer and shallower, delivering heat to the sea surface and to coastal margins. Thinning and recession of marine margins of glaciers and ice caps is expected to accelerate to terrestrial limits, increasing iceberg production, after which glacier retreat may slow on land. Ice shelves will experience continued increase in meltwater production and consequent structural change, but not imminent regional collapses. Marine biota can respond in multiple ways to climatic changes, with effects complicated by past resource extraction activities. Southward distribution shifts have been observed in multiple taxa during the last century and these are likely to continue. Exposed (ice free) terrestrial areas will expand, providing new habitats for native and non-native organisms, but with a potential loss of genetic diversity. While native terrestrial biota are likely to benefit from modest warming, the greatest threat to native biodiversity is from non-native terrestrial species.last_img read more